In order to determine the timing for transferring cells or ending culturing of cells, the culturing state and proliferation state of cells are checked. To check the culturing state and the proliferation state of cells that are adhered to the bottom of a culture vessel, an adhesion area is measured by means of observation from outside a transparent culture vessel by using a microscope or the like (for example, see Patent Literature 1). To measure an adhesion area, an observer makes a count while visually observing an image of the cells acquired via an ocular lens of the microscope, or numerical data are acquired by using a determining program to analyze an image of the cells acquired by using the microscope.
To check the culturing state and the proliferation state of the cells, the cells that are being cultured in a culturing apparatus must be removed from the culturing apparatus together with the entire culture vessel, which is then placed in the microscope. In other words, when, as a result of microscope observation, the culturing state and the proliferation state are not satisfactory, it is necessary to return the culture vessel into the culturing apparatus again and to continue the culturing, and thus, the work performed is wasted and the risk of contamination by other cells such as bacteria or the like and other contaminants such as viruses or the like is increased. On the other hand, if the culturing state and the proliferation state are not checked at an appropriate timing, there is a risk of missing the appropriate timing for transferring the cells.